How to Seal a Basement Leak

Prepare the wall surface by removing any old paint, as the waterproofing compound will not seal correctly on painted surfaces. You can do this by using sandpaper, a stiff brush or a sandblaster, depending upon the amount of paint and other debris that needs to be removed.

Patch any large holes or cracks in the foundation with a mixture of 2 parts cement to 1 part sand. In a bucket, add water to the dry mixture to form a stiff paste.

Apply the patching mixture to the wall using a mason's trowel, taking care to cover the damaged area at least 2 inches past the edge of the crack or hole. Allow to dry for at least eight hours; however, overnight is best.

Wet down the leaking area, using a garden hose with a sprayer. Let the area sit until it is damp and there is no standing water on the surface.

Mix the waterproofing compound as noted on the manufacturer's directions. The mixture can be combined in a large bucket. It should be the consistency of a thick cake batter.

Apply the waterproofing compound to the wall using a stiff brush. Put on the compound in a circular motion, starting at the bottom and working to the top. Feather the edges of the compound, taking care to cover the entire leaking area. Allow it to dry for two or three hours, or until it is dry to the touch, without rubbing off.

Saturate the waterproofed area using a garden hose and allow it to sit overnight.

In the morning, re-wet the waterproofed area and allow it to dry until it is just damp, but not dripping wet.

Put a second coat of waterproofing mixture over the first coat, using the same application technique. Be sure to feather the edges about two inches out from the first coat. Let the area dry completely.